I was also thinking of instead of them being scraped into 3 coal maybe there can be a new resource WOOD. The only purpose WOOD would have is to act as a cleaner burning fuel. In real life COAL produces way more pollution then wood.
Desert areas should not be able to produce trees. There is a reason there is a desert there!
Nanich - sand miners are very unlikely to be able to produce trees, given their -10% aridity value for Food already. It's hard enough to grow Food in the desert, let alone have enough left over to produce a tree!